How much do crops contribute to emissions?

Food production is a major contributor to climate change, so it is critically important to be able to measure greenhouse gas emissions from the food sector accurately. In a new study, we show that the food system generates about 35 percent of total global man-made greenhouse gas emissions.

By breaking down this share, the production of animal foods — meat, poultry, and dairy products, including the cultivation of livestock crops and pastures — contributes to 57 percent of the emissions associated with the food system. Breeding plant-based foods for human consumption contributes 29 percent. The other 14 percent of agricultural emissions come from products that are not used as food or feed, such as cotton and rubber.

We are atmospheric scientists studying the effects of agriculture and other human activities on the Earth’s climate. It is well known that animal food production generates more greenhouse gas emissions than plant-based foods, and therefore shifting to a more plant-based diet is recognized as an opportunity to curb greenhouse gas emissions and climate change.

However, to quantify the potential impact of such a shift, we saw a need for better tools to estimate emissions from individual plant- and animal-based foods, with more details on how emissions are calculated and cover all food-related subsectors, such as land use change and actions. over the farm gate.

Current methods rely on sparse data and simplified representations of many key factors, such as emissions from agricultural land management. They do not treat different subsectors consistently or calculate emissions to produce many specific goods.

To fill these gaps, we have developed a comprehensive framework that combines modeling and various databases. This enables us to estimate the average annual global emissions of the greenhouse gases carbon dioxide, methane and nitrous oxide from the production and consumption of plant and animal based human foods. Currently, our study covers the years 2007-2013. Here are some insights it provides using data representing an average of these years.

Hunger and food security are pressing global challenges. Climate change is a contributing factor.

Greenhouse gases from food production

We considered four major sub-sectors of emissions from plant- and animal-based food production. Overall, we calculated that the food system produces emissions equivalent to about 17.3 billion tons of carbon dioxide annually.

Land use change – clearing of forests for farms and ranches, reducing carbon storage in trees and soil – accounts for 29 percent of total food production of greenhouse gas emissions. A further 38 percent comes from agricultural land management activities, such as plowing fields, reducing soil storage of carbon and treating crops with nitrogen fertilizer. Farmers also burn a lot of fossil fuels to power their tractors and harvesters.

Livestock farming generates 21 percent of greenhouse gas emissions from food production. It includes methane bordering on grazing animals, as well as methane and nitrous oxide released from livestock manure. The remaining 11 percent comes from activities that take place outside the farm gates, such as mining, manufacturing and transporting fertilizers and pesticides, as well as energy consumption in food processing.

Many agricultural activities release carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) into the atmosphere. Some store carbon in plants and soil. CRS

Which foods generate the most greenhouse gas emissions?

Our framework makes it possible to compare how food and food-producing regions affect the Earth’s climate.

Among animal foods, beef is the largest contributor to climate change. It generates 25 percent of total food emissions followed by cow’s milk (8 percent) and pork (7 percent).

Rice is the largest contributor among plant-based foods and produces 12 percent of total greenhouse gas emissions from the food sector, followed by wheat (5 percent) and sugar cane (2 percent). Rice stands out because it can grow in water, so many farmers flood their fields to kill weeds, creating ideal conditions for certain bacteria that emit methane.

This helps explain why South and Southeast Asia have the largest food production-related emissions by region, producing 23 percent of global total. This region is the only place where plant-based emissions are greater than animal-based emissions. South America is the second largest issuer with 20 percent and has the largest emissions from animal food, reflecting the dominance of ranching there.

Among the individual countries, China, India and Indonesia have the highest emissions from plant-based food production, contributing 7 percent, 4 percent and 2 percent of global food-related greenhouse gas emissions, respectively. The countries with leading emissions from animal food production are China (8 percent), Brazil (6 percent), the United States (5 percent) and India (4 percent).

A tractor spreads manure on a dirt field.

Manure injection into a manure field in Lawler, Iowa. Manure is an important source of greenhouse gas emissions from livestock. AP Photo / Charlie Neibergall

How food production affects land use

Our framework also shows that growing animal foods consumes six times as much soil as producing plant-based foods.

Worldwide, we estimate that humans use 18 million square kilometers of land to produce food – about 31 percent of the Earth’s total area, excluding areas covered in snow and ice. Of this, 30 percent is cultivated land, and 70 percent is various types of grazing land.

When we look at how these areas are managed, we estimate that 13 percent of the total agricultural land is used to produce plant-based foods. The other 77 percent is used to produce animal foods, including cultivated fields that grow forage and grazing land. The remaining 10 percent is used to raise other products, such as cotton, rubber and tobacco.

Our study uses a consistent framework to provide a complete assessment of greenhouse gas emissions from food production and consumption, covering all food-related sub-sectors on a local, country, regional and global scale. It can help politicians identify the plant- and animal-based foods that contribute the largest proportions to climate change and the highest-emitting sub-sectors in different places.

Based on these findings, governments, researchers, and individuals can take steps to reduce emissions from high-emission foods in various locations. As UN leaders have stated, it is important to make food production more climate-friendly in order to reduce hunger in a warming world.

This article is republished from The Conversation under a Creative Commons license.

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